The present invention relates generally to the fabrication of semiconductor devices, and more particularly to metal-insulator-metal (MIM) capacitors.
Semiconductors are widely used for integrated circuits for electronic applications, including radios, televisions and personal computing devices, as examples. Such integrated circuits typically use multiple transistors fabricated in single crystal silicon. It is common for there to be millions of semiconductor devices on a single semiconductor product. Many integrated circuits now include multiple levels of metallization for interconnections.
For many years, aluminum has been used for the conductive material comprising the interconnect layers of semiconductor devices. Usually an aluminum alloy with a small amount of copper and silicon is used. For example, a prior art aluminum conductive alloy may comprise 2% silicon to prevent the aluminum from diffusing into the surrounding silicon, and 1% copper, to control electromigration and lead breakage due to Joule""s heat.
The semiconductor industry continuously strives to decrease the size and increase the speed of the semiconductor devices located on integrated circuits. To accomplish these goals, the semiconductor industry is changing from aluminum to copper for metallization layers. Copper has a lower resistivity compared to the resistivity of aluminum, resulting in faster current capability when used as a conductive material. Also, the use of a lower resistivity metal permits decreased widths and thicknesses. Copper exhibits reduced levels of electromigration as compared with aluminum.
The semiconductor industry is also moving towards using low-dielectric constant (k) materials as insulators between conductive leads and the various metallization layers to reduce the overall size of the semiconductor devices.
Using copper as the material for metallization layers has proven problematic because copper has a tendency to diffuse into and through surrounding dielectric layers, contaminating the semiconductor device and possibly rendering it inoperable. To prevent the copper from diffusing, barrier layers and liners are typically used around copper surfaces to protect the dielectric layers. Metallic barrier layers and/or dielectric cap layers are also required on top of the copper surfaces prior to depositing subsequent dielectric layers. Not only do these barrier layers require additional processing steps and materials, they are particularly problematic in MIM capacitors. The barrier layers used often comprise titanium nitride or some other metal (e.g., Ta, W, and others) combined with a nitride (e.g. TaN, WN and others), and these materials have a higher resistance than copper. Thus, the resistance of the metal plates of a MIM capacitor is increased by the use of the barrier layers. Furthermore, dielectric diffusion barriers or cap layers are required over the top of the copper plates prior to depositing the MIM dielectric.
What is needed in the art is a structure and method for reducing the number of barrier layers and liners required when manufacturing MIM capacitors having copper conductive materials. What is also needed in the art is the ability to have more choices for a MIM capacitor dielectric in order to achieve high area capacitances and high quality standards in the dielectric MIM reliability.
These problems are generally solved or circumvented by the present invention, which achieves technical advantages as a MIM capacitor having self-passivating plates. The self-passivation prevents copper out-diffusion and/or copper corrosion or oxidation. The self-passivation is achieved by the formation of a dopant-rich surface layer at the interfaces between Cu and the liners or dielectrics and by the formation of a dopant-rich surface layer with a thin insulating (oxidized) top surface layer of the dopant-rich region on Cu surfaces exposed to the environment (e.g. air).
Disclosed is a method of forming a capacitive plate of a MIM capacitor, comprising forming a capacitive plate, and annealing the capacitive plate to form a dopant-rich region at the edges of the capacitive plate. An insulating region is formed over exposed portions of the dopant-rich region.
Also disclosed is a method of fabricating a MIM capacitor, comprising forming a first capacitive plate and annealing the first capacitive plate to form a first dopant-rich region at the edges of the first capacitive plate. A first insulating region is formed over exposed portions of the first dopant-rich region. A capacitor dielectric layer is deposited, and a second capacitive plate is formed. The second capacitive plate is annealed to form a second dopant-rich region at the edges of the second capacitive plate. A second insulating region is formed over exposed portions of the dopant-rich region.
Further disclosed is a metal-insulator-metal (MIM) capacitor, comprising a first capacitive plate having a dopant-rich region at the edges thereof and an insulating region disposed over a portion of the dopant-rich region. A capacitor dielectric layer is disposed over the first capacitive plate, and a second capacitive plate is disposed over the capacitor dielectric layer and the first capacitive plate. The second capacitive plate has a dopant-rich region at the edges thereof and an insulating region disposed over a portion of the dopant-rich region.
Advantages of the invention include a MIM capacitor requiring fewer metal liners and dielectric liners than in the prior art. The surface roughness of the capacitive plate tops is reduced, resulting in a more reliable MIM capacitor. Fewer processing steps and materials are required than in the prior art. The dopant-rich regions are created by annealing, and the oxide regions over the dopant-rich regions are created by exposure to oxygen. The diffusion of copper into capacitor dielectric and other dielectrics in the MIM capacitor is suppressed by the self-passivating metal plates. The self-passivation effect of the copper alloys used protects the copper during capacitor dielectric deposition because of the insulating or oxidized region formed on exposed portions of the dopant-rich region. The conductivity of MIM capacitor metal plates is significantly increased.